Effects of InGaN/GaN superlattice absorption layers on the structural and optical properties of InGaN solar cells

This article studies metal-organic vapor phase epitaxy-grown InGaN p- ^i-n solar cells with superlattice (SL) absorption layers on c -plane sapphire for the influence of InGaN/GaN SLs on the structural and optical properties of the solar cells. Numerical simulations indicate that conventional p-^i-n solar cells with a 200-nm-thick In0.06 Ga0.94 N absorption layer provide absorption rates as high as 65%. However, experimentally, the optical properties of such an epistructure are deteriorated by the formation of structural defects and result in the fabricated devices having worse photovoltaic characteristics. On the other hand, high-resolution x-ray diffraction and photoluminescence analyses show that solar cells with a SL have improved crystalline quality and can accommodate more indium content than those using an InGaN layer. It was also found that the degree of the exciton localization effect does not rise considerably with increases in the indium content and the SL pair numbers. This could be due to variations in dislocation density, interface roughness, and well width during the SL growth. Using SLs of a reasonable crystalline quality, these fabricated solar cells exhibit improved photovoltaic characteristics.